Kelley Mack, best known for her recurring role as Addy on AMC's "The Walking Dead," has died at the age of 33 following a rare and aggressive form of cancer affecting the central nervous system. Her death was confirmed Saturday in her hometown of Cincinnati, Ohio, by her family and representatives.
Mack, born Kelley Lynne Klebenow, had publicly shared her battle with diffuse midline glioma (DMG), a rare cancer typically seen in children but also known to affect adults. Her agent Julie Smith confirmed the diagnosis and cause of death to USA Today.
"It is with indelible sadness that we are announcing the passing of our dear Kelley," her sister Kathryn Klebenow wrote in a statement posted to the actress's Instagram page. "Such a bright, fervent light has transitioned to the beyond, where we all eventually must go."
Mack passed away peacefully on Saturday evening, surrounded by her mother Kristen and her aunt Karen, according to the family statement. "She will be missed by so many to depths that words cannot express," her sister added.
Actress Kelley Mack, 33, has died suddenly from an aggressive brain cancer after getting vaccinated with mRNA.
The up and coming Hollywood star was pressured into taking the shot to be on set for Chicago Med and other films and commercials.
Kelley was diagnosed with diffuse… pic.twitter.com/2dOyXNHxpZ — Died Suddenly (@DiedSuddenly_) August 6, 2025
The actress revealed her diagnosis in January, explaining that symptoms began in October 2024 with persistent lower back pain. After an emergency room visit in November, scans revealed an abnormal mass in her spinal cord. The diagnosis ultimately led to loss of mobility in both legs following a biopsy.
"Due to the biopsy surgery on my spinal cord, I have lost the use of my right leg and most of my left leg, so I now get around with a walker and a wheelchair," Mack said via Instagram earlier this year. "I am determined and know that this will eventually be a short chapter in my long book."
In March, Mack posted a video of herself walking upstairs during physical therapy. "I've been up and down these stairs now 2x in the past few days," she captioned. "It's a big deal for me."
Mack appeared in five episodes of "The Walking Dead" during its ninth season, playing Hilltop Colony resident Addy. In a 2019 interview with Alternative Mindz, she said, "I was only supposed to be in 2 episodes originally, so I was grateful to have been able to work on five of them."
Her other television credits include guest roles on "Chicago Med" and "9-1-1." She also appeared in films such as "Mr. Manhattan," "Broadcast Signal Intrusion," and "Delicate Arch," and produced a number of short films.
Tributes from colleagues and fans poured in following news of her death. Actress Alanna Masterson wrote, "What an incredible human. So proud to have fought alongside her in our final episode together." Michael E. Satrazemis, a director on "The Walking Dead," added: "A bright light on every level. All my love to those who love her."
"Kelley was such a sweet and happy soul and I'm happy to have met her," wrote co-star Anthony Michael Lopez. "She fought so hard. Rest easy Kelley."
Mack began acting in commercials as a child. Her first film role was in "The Elephant Garden," which won the Student Visionary Award at the 2008 Tribeca Film Festival.
She is survived by her parents, Kristen and Lindsay Klebenow; her siblings Kathryn and Parker; and her grandparents Lois and Larry Klebenow. A memorial service is scheduled for August 16 in Glendale, Ohio.
